1. Field of the Invention
The present invention relates to a fixing and heating device to be used for an electrostatic copying apparatus for heating and fixing a toner image on a copy paper sheet passed through a pair of fixing rollers, and more particularly to temperature control of the fixing rollers.
2. Description of the Prior Art
In one prior art arrangement, fixing rollers are driven to rotate at a relatively high speed suitable for fixing when a power switch is closed. Before the power switch is closed, toner remains residually from a preceding copying operation and solidifies on the fixing rollers, and thereby a pair of the fixing rollers contact with each other. The fixing rollers rotate upon closing the power switch. At this time one fixing roller is not heated at a softening temperature or a melting temperature of the toner, and therefore the solidified toner remaining on the fixing rollers injures the fixing rollers.
Another prior art arrangement comprises a scraper plate for scraping off the toner remaining on the fixing roller to prevent a copy paper from winding around the fixing roller. Since the fixing roller is driven to rotate before the solidified toner remaining between the surface of the fixing roller and the scraper plate is softened and melted, the scraper plate is deformed by rotation of the fixing roller. The toner solidifying on the fixing roller and the scraper plate result in a sound occurring when when the fixing roller begins to rotate. Resultant rotation at a relatively high speed causes the fixing rollers to make a larger noise.
Still another prior art arrangement comprises a fixing roller which begins to rotate at a relatively high speed when the power switch is closed, and the surface of the fixing rollers is heated at a temperature suitable for fixing. Once the fixing rollers are heated at the temperature suitable for fixing, they continuously rotate at a relatively high speed. Therefore, continuous rotation causes damage to the fixing rollers and causes the fixing rollers to make sounds. Further, when a fixing operation is performed as soon as the fixing rollers reach the temperature suitable for fixing and begin to rotate, since the surface temperature of the fixing rollers not yet been made uniform, a disadvantageous fixing state is provided over a copy paper sheet by an insufficient heated temperature or by a poor quality of fixing. Moreover, since the fixing rollers remain stationary until the fixing rollers reach the temperature suitable for fixing, a pair of the fixing rollers tend to be deformed by mutual pressure against each other.
It is an object of the invention to provide a fixing and heating device to prevent the fixing rollers from being injured by residual toner on the fixing rollers.
A more particular object of the invention is to provide a new and improved fixing and heating device for fixing toner images on a copy paper sheet.
These and other objects will become more apparent from the following description and drawings.